Vision Prescription Converter Calculator
Convert between vision prescription formats including diopters, Snellen, and LogMAR. Plus glasses-to-contacts conversion with vertex distance correction.
20/20 Vision Calculator
Convert Snellen visual acuity to LogMAR, decimal, and MAR. Check driving eligibility and compare vision classification across international standards.
⚠️ Medical Disclaimer: This calculator provides educational estimates only. A comprehensive eye exam by an optometrist or ophthalmologist is required for accurate assessment.
years
feet
Binocular (Best Eye)
20/20
Normal Vision
✓ Meets US driving requirement (20/40)
Right Eye (OD)⧉
20/20
Normal Vision — LogMAR 0, Decimal 1
Left Eye (OS)⧉
20/25
Near Normal — LogMAR 0.1, Decimal 0.8
Right LogMAR⧉
0
Logarithm of the Minimum Angle of Resolution (0 = 20/20)
Left LogMAR⧉
0.1
Negative values = better than 20/20 vision
Right MAR⧉
1 arcmin
Min. angle of resolution; letter size ≈ 8.73 mm at 20 ft
Left MAR⧉
1.25 arcmin
Min. angle of resolution; letter size ≈ 10.91 mm at 20 ft
Age-Expected Acuity⧉
20/20
Typical for age 35. Normal decline starts around age 60.
Driving Eligible (US)⧉
Yes
US requirement: 20/40 or better in best eye (with correction)
Snellen ↔ LogMAR Conversion
| Snellen | Decimal | LogMAR | MAR (arcmin) | Classification |
|---|---|---|---|---|
| 20/10 | 2 | -0.3 | 0.5 | Exceptional Vision |
| 20/13 | 1.538 | -0.19 | 0.65 | Exceptional Vision |
| 20/15 | 1.333 | -0.12 | 0.75 | Normal Vision |
| 20/20 | 1 | 0 | 1 | Normal Vision |
| 20/25 | 0.8 | 0.1 | 1.25 | Near Normal |
| 20/30 | 0.667 | 0.18 | 1.5 | Near Normal |
| 20/40 | 0.5 | 0.3 | 2 | Near Normal |
| 20/50 | 0.4 | 0.4 | 2.5 | Moderate Low Vision |
| 20/60 | 0.333 | 0.48 | 3 | Moderate Low Vision |
| 20/70 | 0.286 | 0.54 | 3.5 | Severe Low Vision |
| 20/80 | 0.25 | 0.6 | 4 | Severe Low Vision |
| 20/100 | 0.2 | 0.7 | 5 | Severe Low Vision |
| 20/200 | 0.1 | 1 | 10 | Profound Low Vision / Legal Blindness |
International Driving & Legal Blindness Thresholds
| Country | Driving Requirement | Legal Blindness |
|---|---|---|
| USA | 20/40 | 20/200 |
| UK | 6/12 (≈20/40) | 6/60 (≈20/200) |
| Canada | 20/50 | 20/200 |
| Australia | 6/12 (≈20/40) | 6/60 (≈20/200) |
| EU (avg) | 6/12 (≈20/40) | 6/60 (≈20/200) |
Your Vision vs. Scale
Right: 20/20
Left: 20/25
Planning notes, formulas, and examples
About the 20/20 Vision Calculator
The 20/20 Vision Calculator converts Snellen acuity into LogMAR, decimal acuity, and Minimum Angle of Resolution (MAR). It also compares the result with common driving thresholds and the usual legal-blindness cutoff.
Snellen notation expresses the test distance and the line that was read. For example, 20/40 means the chart line was read at 20 feet when a person with typical acuity could read it at 40 feet.
That makes it easier to compare eye-test results that are written in different formats.
When This Page Helps
Seeing visual acuity in several formats makes it easier to compare eye exams, driving requirements, and research notation. The same reading can look different depending on whether it is written as Snellen, LogMAR, decimal acuity, or MAR.
How to Use the Inputs
- Select your right eye (OD) Snellen fraction from the dropdown.
- Select your left eye (OS) Snellen fraction.
- Enter your age for age-expected comparison.
- Choose whether the reading is corrected (glasses/contacts) or uncorrected.
- Optionally adjust the test distance if your exam used a non-standard distance.
- Review the classification, LogMAR conversions, and driving eligibility results.
- Use the reference table to compare your acuity against the full Snellen scale.
Formula used
LogMAR = log₁₀(Snellen denominator / 20)
Decimal Acuity = 20 / Snellen denominator
MAR = Snellen denominator / 20 (arcmin)
Corrected Snellen at distance d: 20/(denom × 20/d)Example Calculation
Result: Right: LogMAR 0.10, Left: LogMAR 0.18 — Near Normal vision, meets driving requirement
Both eyes are slightly below 20/20 but well within the 20/40 US driving threshold. At age 45, this is within normal range.
Tips & Best Practices
- Always record whether your reading is corrected or uncorrected — they tell very different stories.
- LogMAR is preferred in clinical research because it allows proper statistical analysis.
- Binocular vision is typically one line better than your best monocular eye.
- If your acuity differs significantly between eyes (2+ lines), mention it to your eye doctor.
- Snellen fractions are not true fractions — 20/40 is not "half" of vision.
- Digital screen distance acuity (20 inches) uses a different chart than standard Snellen (20 feet).
Understanding Visual Acuity Measurements
Visual acuity is typically the first test performed in any eye examination. The Snellen chart, invented by Dutch ophthalmologist Herman Snellen in 1862, remains a widely used reference system. Modern eye care also uses notation systems including LogMAR, decimal acuity, and MAR, each with advantages for different clinical and research contexts.
When to Seek Professional Help
While this calculator helps interpret your numbers, certain findings warrant prompt professional attention. A sudden drop in acuity in one eye could indicate retinal detachment, macular degeneration, or vascular occlusion. A difference of three or more lines between eyes (anisometropia) may affect binocular function. Any acuity below 20/40 that hasn't been evaluated should prompt an eye exam, especially for drivers.
Vision Correction Options by Acuity Level
Mild refractive errors (20/25 to 20/40) are typically correctable with glasses, contacts, or refractive surgery. Moderate errors (20/50 to 20/80) usually respond well to correction but may indicate underlying conditions. Severe low vision (20/100+) often requires specialized low-vision aids, magnification devices, and rehabilitation services beyond standard correction.
Sources & Methodology
Last updated:
Methodology
This page converts the entered Snellen fraction into decimal acuity, MAR, and LogMAR using standard visual-acuity relationships. The driving and legal-blindness notes are broad reference markers only and are not a substitute for the rules in a specific state or country.
It is best used as a notation-conversion and interpretation aid after an eye exam, not as a stand-alone eye-health assessment. Visual acuity is only one part of vision, and this page does not assess visual field, contrast sensitivity, ocular disease, or refraction.
Sources
- Visual Acuity (American Optometric Association) — AOA overview of Snellen visual acuity and what 20/20 notation means.
- Healthy Vision Starts With a Dilated Eye Exam (National Eye Institute) — NEI patient guidance used for the page’s eye-exam context and limitation notes.
Frequently Asked Questions
20/20 means you can see at 20 feet what a person with normal vision sees at 20 feet. It is the baseline for "normal" acuity but not perfect — some people achieve 20/15 or even 20/10.
No. 20/20 is the standard baseline. Many people, especially younger individuals, can see 20/15 or 20/10. "Perfect" vision also requires good contrast sensitivity, color vision, and peripheral vision.
LogMAR (Logarithm of the Minimum Angle of Resolution) provides a linear scale for statistical analysis. A LogMAR of 0 equals 20/20; negative values are better than 20/20; positive values are worse.
Most US states require 20/40 or better in at least one eye, with or without correction. Some states allow 20/50 or 20/60 with restrictions like daylight-only driving.
In the US, legal blindness is generally defined as best-corrected visual acuity of 20/200 or worse in the better eye, or a visual field of 20 degrees or less.
Age-related acuity decline (presbyopia) typically begins around age 40 for near vision. Distance acuity may decline after age 60, with 20/25 to 20/30 being common in healthy older adults.
Snellen uses 20 feet (US) while metric uses 6 meters. 20/20 equals 6/6. To convert, divide both numbers by 3.28 (feet to meters).
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